Here's a simple forehatch rain cover using an inexpensive beach umbrella. I'm not sure if it would fit on the newer boats, but it should work like a charm on any classic Mac 25 equipped with a bow pulpit and lifelines.

Just cut the umbrella tube as short as you can while still allowing the runner to close all the way without falling off the end, deploy the umbrella over your foredeck hatch and pull it down against the lifelines snugly. Mark the shaft where it touches your headliner and drill a hole large enough to insert a 6" screw. When rain threatens, open the umbrella and center it over the forward edge of the hatch above the lifelines, pull the shaft down into the cabin and insert the screw through the hole and rest it against the cabin top. A wing nut on the end should provide enough friction to keep the screw from vibrating backward, or you can close the hatch against the umbrella shaft to lock it in place.

Depending on the umbrella quality and frequency of use, you should be able to get a season or two out of it before needing replacement. During fall clearance sales, I've been able to pick these umbrellas up for as little as $5 each.